A typical example of a charge controlled ink jet recording system is disclosed in U.S. Pat. No. 3,596,275 issued to Richard G. Sweet wherein a pressurized ink is supplied to an ink injection head which produces an oscillation of a given period in the pressure of the pressurized ink. An ink stream issuing from the nozzle of the head is separated into ink particles with a given period, at a location which is a given distance advanced from the nozzle. A charging electrode is located at the location where the ink stream is separated into particles. By applying a charging voltage to the electrode as the ink is converted into particles, the ink particles can be charged. The charged ink particle is then deflected in a deflecting electric field for impingement upon a record paper. Non-charged ink particles move straightforward to be trapped by a catcher to be returned to an ink vessel.
One of problems which are experienced in the art of ink jet recording relates to that of an offset in the deflection of ink particles or an offset in the position where a record is made by the ink, which may result from a member of factors including a fluctuation in the temperature or pressure of the ink, inaccuracies in the dimension of the ink injection nozzle, the presence of dirts deposited on the nozzle or the existence of solidified ink, among other factors. A variety of apparatus for detecting deflection is employed in order to detect such offset. A related Japanese Laid-Open Patent Application No. 108167/1983 assigned to the same assignee as the present invention discloses a deflection detecting apparatus which utilizes a detector unit having an opening in its front surface through which flying ink particles may pass and an electrode disposed within the unit for detecting the charged ink particles. In order to establish a print position of the charged ink particles on a platen which carries a record paper, the detector unit is supported by a position adjusting mechanism which includes a link arm, a coiled spring and an adjusting screw. Tightening the screw lowers the detector unit while loosening the screw causes the detector unit to be raised by the resilience of the coiled spring. This achieves a vertical adjustment of the location of a detecting electrode relative to the platen. The amount of deflection of ink particles is adjusted so that the charged ink particles pass by or impinge upon the edge of the detecting electrode. In this manner, the charged ink particles may be caused to impinge upon the platen (or the record paper carried thereby) at a given location, by controlling the elevation of the detector unit by means of the adjusting screw and controlling the magnitude of the charge so that the charged ink particles reach the edge of the charge detecting electrode of the detector unit.
The deflection detecting apparatus of the kind described presents a variety of problems including the requirement for the provision of an increased space volume for the installation of the apparatus, the need for a complex positioning mechanism for the detecting electrode of the unit, the occurrence of chattering or the necessity for a time and labor consuming adjusting operation. By way of example, in the aforesaid Japanese Laid-Open Patent Application, the apparatus utilizes a bulky mechanism to support the detector unit, and thus requires an increased space volume for its installation.
A deflection detecting apparatus of the kind described is connected to a charge detector circuit which may comprise an integrator and a comparator, for example, and which is operable to detect the occurrence or not of impingement of the charged ink particles onto the detecting electrode in a manner such that the occurrence of impingement or the charge is detected if an integrated voltage is equal to or greater than 2 volts and the absence of impingement is determined or the detection of the charge is denied for an integrated voltage less than 2 volts. However, it will be appreciated that there is a suspension of an ink mist within the volume in which the detecting electrode is received, the mist wetting the internal wall surface or a support associated with the electrode. The ink which is deposited in this manner may cause a leak path from the detecting electrode or a short-circuit to the ground, resulting in a detection error or the inability of detection.
By way of example, in the deflection detecting apparatus disclosed in the aforesaid Japanese Laid-Open Patent Application, a diamond-shaped detecting electrode is centrally supported by a horizontally extending conductor pin. The adjustment of the deflection is terminated when a proper amount of deflection of the charged ink particles is obtained, which occurs when the charged ink particles which have been impinging upon the upper edge of the electrode are deflected to pass slightly over the upper edge or conversely when the charged ink particles which have been passing over the upper edge are deflected to impinge upon such edge. It will be appreciated that during the adjusting process, the charged ink particles impinge upon the upper edge of the electrode, and this allows the ink to flow therealong to the conductor pin and thence to an external lead connection. In the course of such flow, it may contact with the ink wetted wall surface to cause a leak path from the electrode or a short-circuit to the ground.
In the cited Application, the formation of such leak path or the short-circuit to the ground is prevented by interposing a partition between a portion of the conductor pin which is connected to an external lead and the detecting electrode, and passing the conductor pin through an opening formed in the partition to avoid a contact between the conductor pin and the partition. The provision of the partition stands in the way to a flow of an ink mist or ink spray to a portion of the conductor pin which is connected to an external lead, thus reducing a wetting of the entire pin by the ink. However, during a prolonged period of use, an accumulation of ink on the electrode is transferred to the conductor pin, which gradually increases its volume to move along the conductor pin into contact with the partition and merges with the ink which is wetting the partition, again causing a leak path from the electrode or a short-circuit to the ground. In particular, when a manner of operation is used in which an ink which has travelled to and is contained in the detecting unit in the process of detecting and adjusting the amount of deflection is discarded and a quantity of ink which remains in an ink circulating system is injected into the opening of the detector unit for a given time interval either before or after the detection or adjustment of the deflection so that stale ink is consumed rapidly in order to permit the viscosity of the ink to be controlled, an ink spray or mist which is generated upon impingement of the ink particles on the internal wall of the unit produces a wetting of the electrode and the conductor pin, leading to a premature occurrence of the leak path or the short-circuit to the ground.
In the absence of such leak path or short-circuit, noise voltages may be induced on the detecting electrode if the charged ink particles do not impinge upon the electrode and the charge detector circuit may produce an integrated voltage on the order of 1 volt. It will thus be seen that the integrated voltage will be low in the presence of a leak path while an increased magnitude of noise voltages will be present in the absence of such leak path. Accordingly, in the design of the charge detector circuit, there is a reduced allowance of the detected voltage which may be utilized to discriminate the presence and absence of charge against each other, resulting in a high probability that a detector error may occur.
In addition, the impingement of the charged ink particles upon the detecting electrode produces an ink spray or mist, marring the unit around the opening with the ink. If the amount of such ink deposition increases, it may flow down the external surface of the wall adjacent to the opening, thus marring the printer. This results in the need to clean around the deflection detecting apparatus frequently. It will be appreciated that the elimination of an ink marring of the printer represents a time and labor consuming operation.